Electronic beat producing device



p 6, 1966 D. A. ESAKOV ETAL 3,271,670

ELECTRONIC BEAT PRODUCING DEVICE Filed April 2, 1962 5 SheetsSheet 1 FIG. I

FIG. 2

INVENTOR.

DANIEL A. ESAKOV WILLIAM J. HILDEBRANDT BY ULQQL QW PLM 4 M ATTORNEYS Sept. 6, 1966 D. A. ESAKOV ETAL 3,271,670

ELECTRONIC BEAT PRODUCING DEVICE 5 Sheets-Sheet 3 Filed April 2, 1962 United States Patent 3,271,670 ELECTRGNHC BEAT PRODUCING DEVl CE Daniel A. Esakov, West Hartford, and William J. Hildebrandt, Weatogue, Conn, assignors to Connecticut Technical Corporation, Hartford, Comm, a corporation of Qonnecticut Filed Apr. 2, 1962, Ser. No. 184,366 6 mantis. Cl. 324--68) This invention relates to electronic timers of the type designed to provide a series of impulses or beats at a given frequency, and deals more particularly with such a timer having a control whereby the frequency of the impulses or beats may be readily varied over a wide range.

The electronic timer circuit with which this invention is in part concerned finds particular utility in a metronome wherein the electrical impulses produced are converted into audible'sounds such as ticks or claps by a sounding mechanism and/or into visible signals such as light flashes by a suitable light arrangement. The invention has therefore for convenience been described in detail below as applied to a metronome, but it is to be understood that various parts of the metronome may be used in other applications. This applies particularly to the timing circuit which may be used in many different devices requiring a source of time-marking electrical impulses.

The general object of this invention is to provide a simple electronic timing device for producing a series of electrical impulses or beats and wherein the frequency of such impulses may be varied if desired over a relatively wide range by means of an easily operated manual control.

Another object of this invention is to provide an electronic timing device of the foregoing character wherein each of said impulses or beats consists of a burst of high frequency oscillations which when used to drive a sounding device causes a corresponding high frequency vibration of the armature or the like of the sounding device to produce a highly audible and desirable sharp sound in the nature of a click, tick or clap, and which when use-d to drive a neon lamp causes it to be lighted during the burst to produce a bright visual indication.

Another object of this invention is to provide an electronic timing device of the foregoing character which may be battery operated and wherein the drain on the battery is such as to produce an exceptionally long battery life.

Another object of this invention is to provide an electronic timing device of the foregoing character including an electromechanical sounding device particularly adapted to convert the high frequency bursts of the timing circuit into audible sharp sounds and wherein the timing circuit and sounding device are so constructed and arranged that part of the sounding device constitutes part of the timing circuit with a resulting economy in parts and operation.

A more specific object of this invention is to provide a portable, light weight, transistorized and battery operated metronome which may be designed to provide either an audible or a visible indication, or both, of timing intervals or beats and wherein the frequency or length of the timing intervals may be varied in a continuous fashion over a Wide range.

Other objects and advantages of the invention will be apparent from the following description and from the accompanying drawings forming a part thereof.

The drawings show preferred embodiments of the invention and such embodiments will be described, but it will be understood that various changes may be made from the construction disclosed, and that the drawings and description are not to be construed as defining or limiting the scope of the invention, the claims forming a part of this specification being relied upon for that purpose.

Of the drawings:

ice

FIG. 1 is a perspective view showing the outward appearance of a metronome which may employ the electronic circuit and other elements of the present invention.

FIG. 2 is a schematic wiring diagram of a device embodying the present invention.

FIG. 3 is an elevational view of a combined transformer and sounding device which may be used with the device of FIG. 2.

FIG. 4 is an illustration of various pertinent wave forms occurring in different parts of the device of FIG. 2.

FIG. 5 is an illustration of the collector voltage and emitter voltage wave forms produced in the device of FIG. 2 and drawn on a time scale greatly reduced from that of FIG. 4.

FIG. 6 is a schematic Wiring diagram of a device comprising an alternative embodiment of this invention and generally similar to that of FIG. 2 except for a relocation of the elements associated with the transistor emitter and base terminals.

In accordance with the broader aspects of the invention there is provided a normally free running oscillator which is combined with circuit means for automatically and alternately quenching and permitting operation of the oscillator. During such times as the quenching means is ineffective to quench the oscillator, the oscillator operates to produce an oscillatory output signal and during such times as the quenching means is so eifective operation of the oscillator is prevented so that no oscillations occur. The result is an output signal which constitutes a repetitive series of oscillation bursts which are time spaced from each other by the intervals during which the quenching means are effective. These time spaced bursts of oscillations may be used for various timing purposes and in one more specific aspect of the invention are used to drive a sounding device and/ or a neon lamp as in a metronome to produce audible and/ or visible indications or beats. A device built in accordance with the invention may also include, and preferably does include, means for adjusting the quenching means to vary the duration of the quench ing intervals and therefore the length of time occurring between successive oscillation bursts. The use of oscillation bursts to drive the sounding device or neon lamp of a metronome or the like has been found to produce greatly improved results over prior metronomes wherein a single output pulse drives the sounding device and/or neon lamp during each beat. The bursts of oscillations drive the sounding device in an oscillatory manner to produce a sustained and loud sound throughout the duration of the bursts and the oscillatory nature of the bursts also cause the neon lamp to be lighted at both electrodes to produce an intense flash.

A self-quenching oscillator made in accordance with the broader aspects of this invention may take various different forms, but when used as part of a metronome it is preferably a transistorized and battery powered device which enables the same to be made of small size and packaged in a portable case such as shown in FIG. 1. This latter figure illustrates a metronome comprising a generally pyramidal-shaped case 10 having on its front surface a neon lamp 112 and a calibrated dial 14. The dial 14 is manually rotatable relative to the case and as hereinafter described is associated with both a switch for turning the device on and off and an adjustable circuit element for varying the length of the quenching intervals and accordingly the frequency of the ticks or beats.

The presently preferred form of the present invention is shown by the schematic diagram of FIG. 2. Referring to this figure, the circuit therein shown includes a transistor 16 illustrated as being of the N-PN type and including a collector terminal 18, an emitter terminal 20 and a base terminal 22. Connected to the collector terminal 18 is one end of the primary coil 24 of a transformer indicated generally at 26. The other end of the primary coil 24 is connected through a switch '30 to the positive side of a source of direct current voltage 3 2 which may conveniently be a dry cell or a mercury cell. The transformer 26 also includes a secondary coil 28 which is connected at one end to the base terminal 22 and at its other end is connected to the negative side of .the voltage source 32 through a current limiting resistor 34. The dots associated with the two coils 24, 28 indicate ends of the coils having like polarity and from this it will be noted that the base terminal 22 is inductively coupled to the collector terminal 18 in a regenerative feedback manner.

From the foregoing it will be noticed that if the emitter terminal 20 were now to be connected directly to the negative side of the voltage source 32, the result would be a free running blocking oscillator. The operation of this oscillator would be as follows: At the start of a cycle the base terminal 22 is at the same potential as the emitter and therefore only very little current flows through the collector terminal 18. This small current, however, also flows through the primary coil 24 and induces a voltage across the secondary coil 28 which drives the base terminal 22 positive with respect to the emitter terminal 20. More current will therefore flow through the collector terminal 18 and thereby increase the induced voltage in the secondary coil 28 and further increase the potential of the base terminal 22 relative to the emitter. The result is a cumulative buildup in the collector current which continues until either the transistor or the transformer saturates. As soon as the collector current ceases to increase and starts decreasing the voltage across the primary coil 24 reverses in polarity .and this change is fed back through the inductive coupling with the secondary coil 28 to produce a negative voltage on the base which tends to turn the transistor off and accelerates the decrease in collector current. As the collector current approaches zero its rate of decrease lessens and the voltage fed back to the base by means of the secondary coil gradually disappears so that eventually the collector current will again start to increase and the cycle repeats.

In the circuit of FIG. 2, however, the emitter 20 is not connected directly to the negative side of the voltage source 32, but instead a quenching means is interposed between the emitter terminal and the voltage source which quenching means operates to alternately prevent and permit operation of the oscillator in accordance with a definite time pattern. This quenching means includes a capacitor 3 6 connected between the emitter terminal 20 and the negative side of the voltage source 3-2 so as to be charged by the emitter current. Also connected to the emitter terminal 20 is a resistance which serves to provide a leakage path for the charge on the capacitor 36. In the present case this resistance comprises two potentiometers 38 and 40 connected in series with each other and in parallel with the capacitor 36 as shown, and also includes another potentiometer 41 connected in parallel with the capacitor 36 as shown. The potentiometer 40 is manually adjustable to change the frequency of the occurrence of the oscillation bursts produced by the device and where the device is incorporated in a metronome such as shown in FIG. 1, the wiper of the potentiometer is preferably attached to the same shaft as the switch 30, as indicated by the broken line 42, and this shaft is controlled by rotation of the knob 14 so that the latter knob may be used both to turn the metronome on and off and to vary the beat frequency. The potentiometer 38 is used to calibrate the quenching circuit so that the markings on the low heat rate portion of the dial 1-4 may be made to accurately correspond to the low beat rates or frequencies represented by such markings. The potentiometer 41 is likewise used to calibrate thequenching circuit so that the markings on the high heat rate portion of the dial 14 may be made to accurately correspond to the high heat rates or frequencies represented by such markings.

The operation of the entire circuit shown in FIG. 2

may be understood by referring to such figure and to FIGS. 4 and 5 which show the wave forms occurring at various different points in the system. Assuming that the switch 30 is normally open as shown in FIG. 2 and considering the negative side of the voltage source 32 to be the zero or reference potential, all points in the circuit will be at such zero potential prior to the closing of the switch 30. The device is turned on by closing the switch 30 and this impresses the source voltage across the circuit including the primary coil 24 of the transformer 36. The inductance of the primary coil opposes the source voltage so that the collector terminal 18 initially remains substantially at Zero potential. As current starts to flow through the primary coil 24, it induces a voltage across the secondary coil 28 which is in such a direction as to make the base terminal 22 positive with respect to the emitter terminal 20. This turns on the transistor and permits more current to flow through the collector and primary coil and this, in turn, through the inductive coupling with the secondary coil applies more positive voltage to the base terminal to still further increase the collector current in a cumulative manner. During this cumulative process the collector current increases at a fairly uniform rate so that the voltage drop across the primary coil remains substantially constant and the collector potential remains substantially zero. After the collector current reaches a certain high value as a result of the cumulative buildup process either the transistor becomes saturated so that further increases in base potential will not increase the collector current or the transformer becomes saturated so that further increases in collector I current will not increase the base potential. As a result of either of these events, the increasing nature of the collector current is terminated and this in turn causes the induced voltage across the secondary coil to drop toward zero.

This dropping of the induced voltage across the secondary coil causes the voltage of the base terminal to fall below the potential of the emitter with the effect that it tends to turn off the transistor and causes the collector current to rapidly decrease. This decrease in the collect-or current induces a reverse voltage across the secondary coil which causes the base terminal to be driven below zero potential. At the same time the decreasing nature of the collector current induces a reverse voltage across the primary coil which causes the collector potential to rise above the positive potential of the source 32. As the collector current approaches zero the induced reverse voltages across the primary and secondary coils disappear until a point reached where the collector current starts to increase and a new cycle is started.

Each time a cycle is repeated, as described above, current flows through the emitter terminal 20 and charges the capacitor 36 during the major portion of the cycle. During the terminal portion of each cycle little emitter current flows and some discharging of the capacitor will occur through the potentiometers 38, 40 and 41, but for each cycle the amount of charging is substantially greater than that of the discharging so that the charge on the capacitor is gradually increased throughout a series of repetitive cycles.

As the charge on the capacitor 36 builds up the emitter potential correspondingly rises with the result that the collector voltage swing is progressively lessened. Nevertheless, as the emitter potential rises due to the charging of the capacitor 36 it eventually reaches a point where it is larger than the induced positive voltage on the base terminal so that it quenches the oscillations of the collector current and voltage by preventing the transistor from being turned on by the induced base potential.

After this quenching of the oscillating action by the capacitor 36 the charge on the capacitor slowly leaks off through the potentiometers 38 and 40. As the emitter potential approaches zero, collector current will again start to flow and again intiate oscillations in the collector current. As indicated somewhat generally in FIG. 5, the result of this is that during the time the capacitor 36 is charging the oscillator will operate to produce a burst of oscillations in the collector voltage or current and during the time the capacitor is discharging the oscillations will be eliminated. The result is bursts of oscillations in the collector voltage or current which are separated by the discharge time of the capacitor. As mentioned, this discharge time can be varied by the potentiometer 40 to vary the frequency at which the oscillation bursts are repeated.

When the circuit shown in FIG. 2 is used as a metronome, the output signal appearing across the primary coil 24 of the transformer is converted into audible sounds by a suitable transducer and preferably the transformer 26 comprises an integral part of the transducer to effect an economy of parts used in the metronome. The particular transducer or sounding device used in the preferred embodiment of the invention is shown in FIG. 3 and includes an iron core 44 and a bobbin 46 on which is wound the primary and secondary coils 24 and 28. The iron core 44 and the coil carrying bobbin 46 therefore constitute the transformer 26 illustrated in FIG. 2. Associated with the core 44 is a movable armature 48 having a leg 50 which extends into the core of the bobbin 46. The other two arms of the armature 48 are disposed respectively adjacent the ends of the two arms 52 and 54 of the core 44 so that the core and the armature together provide a low reluctance flux path for the flux generated by the coils 24 and 28. The armature 48 is normally spaced from the core 44 by a small air gap and is moved back and forth relative to the core when the primary coil 24 is energized by a burst of oscillations as described above. Attached to the armature 48 is a suitable sounding device, which in the illustrated case is a phenolic diaphragm 56, which couples the movement of the armature to the air to produce an audible click or beat when the armature vibrates.

In the illustrated case the transformer core 44 is secured to a generally L-shaped bracket 58 secured at one end to the base of the case by a screw 60 which extends through the case, a spacer 62 and the diaphragm 56 and threadably engages the bracket 58. The other end of the bracket 58 threadably engages the upper end of an elongated screw 64 which extends through the base of the case 10, a spacer 66 and the diaphragm 56. Between the bracket 58 and the diaphragm 56 the screw 64 carries a coil compression spring 68 which biases the bracket 58 upwardly and presses the diaphragm 56 into firm engagement with the spacer 66. By turning the screw 64 in one direction or the other the spacing between the armature 48 and the core arms 52 and 54 may be varied to vary the loudness of the click or tick produced by each oscillation burst, and the sound may be eliminated entirely by rotating the screw 64 in such a direction and to such an extent as to completely close the gap normally existing between the core and the armature.

In addition to being used to drive an electromechanical sounding device such as that shown in FIG. 3, the circuit of FIG. 2 may also be used to provide a visual indication of the oscillation bursts produced across the primary coil 24. As shown in FIG. 2 this is accomplished by connecting to one end of the primary coil 24 an autotransformer coil '70 and by connetcing a neon lamp 12 and a current limiting resistor 72 in series across the other end of the aut-otransformer coil 70 and the other end of the primary coil 24. In the transducer shown in FIG. 3, the autotransformer coil 70 is wound on the same bobbin 46 as the primary and secondary coils 24 and 28 and acts to step up the voltage appearing across the primary coil 24 to a suflicient extent to light the neon lamp 12. It is to be understood, however, that the neon lamp 12 and the autotransformer coil 70 are not essential to the basic operation of the circuit shown in FIG. 2

and may be eliminated in cases where a light signal is not necessary or desired.

In this regard it should also be noted that the value of the resistor 34 will have an effect on the strength of the audible and visable signals produced by the metronome. Increasing the value of this resistor increases the number of oscillations required to charge the capacitor 36 to the point where further oscillation is prevented, but also decreases the amount of collector and emitter current which flows during each cycle. As a result the light signal is improved because of the increased number of cycles applied to the neon lamp 12, but the loudness of the sound emitted from the sounding device is reduced because of the reduction in the strength of the current or power supplied thereto. Decreasing the value of the resistor 34 has the opposite effect of decreasing the value of the light signal by decreasing the number of cycles in each oscillation burst, but at the same time increases the loudness of the audible signal by increasing the power supplied to the sounding device. Since the audible signal is generally considered more important than the visable signal the resistor 34 is preferably of such a value as to provide the best audible signal and may be omitted entirely if desired.

As shown in the device of FIG. 2, the quenching capacitor 36 and the parallel leakage branches comprised of the potentiometers 38, 40 and 41 are connected between the emitter terimnal and the negative side of the voltage source 32. These elements together with the resistor 34, if any, connected between the base terminal and the negative side of the battery determined the effective biasing voltage, or base to emitter voltage, applied to the transistor and serve among other things to control the number of cycles in each burst of oscillation and the beat frequency. Substantially, the same biasing effect may be obtained, however, by interchanging the positions of these elements and the resistor 34 so that the capacitor 36 and its two parallel resistance leakage paths comprised of the potentiometers 38, 4t) and 41 are connected between the base terminal of the transistor and the negative side of the source and the resistor 34, if used, is connected between the emitter terminal and the negative side of the source.

A device utilizing this circuit arrangement is illustrated in FIG. 6, in which figure the same reference numerals have been applied to the various elements as applied to corresponding elements of FIG. 2. From this it will be evident that the operation of the FIG. 6 device is essentially similar to the operation of the FIG. 2 device and therefore need not be repeated. The removal of the capacitor 36 and potentiometers 38, 40 and 41 from the emitter circuit does, however, result in a generally stronger or more powerful signal to the sounding device to produce a louder sound output and for this reason the circuit of FIG. 6 is generally preferred to the circuit of FIG. 2.

The invention claimed is:

l. An electronic metronome comprising a transistor having emitter, base and collector terminals, means providing a source of direct current voltage, a transformer having a primary coil connected between said collector terminal and one side of said voltage source and also having a secondary coil connected between said base terminal and the other side of said voltage source, said primary and secondary coils being so arranged as to provide at least part of a regenerative feedback path between said collector and base terminals which causes oscillations in the current flowing through said collector terminal, a resistance and a capacitance connected in parallel between said emitter terminal and said other side of said voltage source for alternately quenching and permitting said oscillations of said collector current so as to produce successive burts of such oscillations, said transformer including an iron core having an armature movable in response to flux changes produced by energization of said transformer by said bursts of oscillations, and a sounding device connected to said armature for converting the movement of said armature into audible sounds.

2. An electronic metronome comprising a transistor having emitter, base and collector terminals, means providing a source of direct current voltage, a transformer having a primary coil connected between said collector terminal and one side of said voltage source and also having a secondary coil connected between said base terminal and the other side of said voltage source, said primary and secondary coils being so arranged as to provide at least part of a regenerative feedback path between said collector and base terminals which causes oscillations in the current flowing through said collector terminal, a parallel re sistance and capacitance connected in series with said secondary coil for alternately quenching and permitting said oscillations of said collector current so as to produce successive bursts of such oscillations, said transformer including an iron core having an armature movable in response to flux changes produced by energization of said transformer by said bursts of oscillations, and a sounding device connected to said armature for converting the movement of said armature into audible sounds.

3. An electronic device for repetitively producing time spaced bursts of oscillations in an output signal, said device comprising a transistor having base, emitter and collector terminals, a transformer having a primary coil connected in series with said collector terminal and a secondary coil connected in circuit with one of the other of said terminals in such a manner that voltage signals appearing across said primary coil produce changes in the base to emitter voltage in a regenerative feedback fashion to normally produce an oscillating current through said collector and emitter terminals, a capacitor connected in circuit with one of said collector and emitter terminals so as to be charged by the current passing therethrough and so that the charge thereon varies said base to emitter voltage and thereby tends to reduce current flow between said collector and emitter terminals as said charge increases, said capacitor having such a value as to be incrementally charged as a result of each oscillation of said oscillating current and so as to attain a charge sufficient to block further oscillations after a plurality of oscillations, a resistance connected in parallel with said capacitor for permitting the charge to leak therefrom, said resistance being adjustable to vary the rate of discharge of said capacitor, said transformer including an iron core on which said primary and secondary coils are wound, an armature movable relative to said iron core in response to flux changes produced by energization of said transformer, and a sounding device connected to said armature for converting the movement of said armature into audible sounds.

4. An electronic device as defined in claim 3 further characterized by said transformer including an autotransformer coil connected in circuit with said primary coil, and a neon lamp connected in circuit with said autotransformer coil.

5. An electronic device for repetitively producing time spaced bursts of oscillations, said device comprising a transistor having base, emitter and collector terminals, a source of direct current voltage, collector circuit means between one side of said voltage source and said collector, emitter circuit means between the other side of said voltage source and said emitter, base circuit means between said other side of said voltage source and said base, at least some parts of said last two circuit means also providing a circuit between said emitter and said base, said collector circuit means including a primary coil inductively coupled with a secondary coil forming part of one of the other two circuit means and which coils are arranged so that an output voltage signal appearing across said primary coil changes the base to emitter voltage in a regenerative feedback manner to cause oscillation of said output voltage and of the current flowing through said emitter and collector terminals, one of said other two circuit means including a capacitor which is incrementally charged by the current flowing through the associated transistor terminal during each oscillation and which imposes a voltage between said emitter and base terminals in opposition to the feedback voltage imposed between the same terminals by said secondary coil, said capacitor being of such a size that after a given number of oscillations the voltage thereacross will exceed the feedback voltage of said secondary coil and prevent said feedback voltage from initiating any further oscillations, a resistance connected with said capacitor for permitting leakage of the charge therefrom to gradually reduce the voltage across the capacitor to the point where oscillations may again take place, said resistance being adjustable to vary the rate of discharge of said capacitor, said primary and secondary coils being wound on an iron core, an armature movable relative to said iron core in response to flux changes in said iron core produced by energization of said coils, and a sounding device connected to said armature for converting the movement of said armature into audible sounds.

6. An electronic device as defined in claim 5 further characterized by an autotransformer coil having one end connected to one endof said primary coil, and a neon lamp connected across the other end of said autotransformer coil and the other end of said primary coil.

References Cited by the Examiner UNITED STATES PATENTS 2,097,066 10/1937 Hoover 324-68 2,522,492 9/1950 Anderson 32468 3,005,158 10/1961 Spinrad 30788.5 3,038,120 6/1962 Bernstein et al 32468 3,100,283 8/1963 Makow 331174 OTHER REFERENCES Transistor Blocking Oscillator, (Fairchild Corp), Solid State Journal, pages 64 and 66-68, dated March 1961.

WALTER L. CARLSON, Primary Examiner.

FREDERICK M. STRADER, Examiner.

C. W. HOFFMANN, M. J. LYNCH,

Assistant Examiners. 

1. AN ELECTRONIC METRONOME COMPRISING A TRANSISTOR HAVING EMITTER, BASE AND COLLECTOR TERMINALS, MEANS PROVIDING A SOURCE OF DIRECT CURRENT VOLTAGE, A TRANSFORMER HAVING A PRIMARY COIL CONNECTED BETWEEN SAID COLLECTOR TERMINAL AND ONE SIDE OF SAID VOLTAGE SOURCE AND ALSO HAVING A SECONDARY COIL CONNECTED BETWEEN SAID BASE TERMINAL AND THE OTHER SIDE OF SAID VOLTAGE SOURCE, SAID PRIMARY AND SECONDARY COILS BEING SO ARRANGED AS TO PROVIDE AT LEAST PART OF A REGENERATIVE FEEDBACK PATH BETWEEN SAID COLLECTOR AND BASE TERMINALS WHICH CAUSES OSCILLATION IN THE CURRENT FLOWING THROUGH SAID COLLECTOR TERMINAL, A RESISTANCE AND A CAPLACITANCE CONNECTED IN PARALLEL BETWEEN SAID EMITTER TERMINAL AND SAID OTHER SIDE OF SAID VOLTAGE SOURCE FOR ALTERNATELY QUENCHING AND PERMITTING SAID OSCILLATIONS OF SAID COLLECTOR CURRENT SO AS TO PRODUCE SUCCESSIVE BURTS OF SUCH OSCILLATIONS, SAID TRANSFORMER INCLUDING AN IRON CORE HAVING AN ARMATURE MOVABLE IN RESPONSE TO FLUX CHANGES PRODUCED BY ENERGIZATION OF SAID TRANSFORMER BY SAID BURSTS OF OSCILLATIONS, AND A SOUNDING DEVICE CONNECTED TO SAID ARMATURE FOR CONVERTING THE MOVEMENT OF SAID ARMATURE INTO AUDIBLE SOUNDS. 